Bleaching process and bleach



Patented July 7, i936 BEEACWNG ERQQESS AND BLEACH Wilhelm Hirschmnd, Eerlieley, case, aseig nor to Great Western Electro-ilhemical (Company, San Francisco, @alii. a corporation oi (Caliice-1min N Drawing. Application April 3, H32,

erlai No. b93391 This invention is concerned with the treatment of solutions of calcium salts such as a calcium hypochlorite solution to provide water clear solutions which maintain a substantially constant alkalinity even though the solutions are used in processes developing acids.

The maintenance of an alkaline state in the bleach liquor is essential since the ideal bleaching reaction in alkaline solutions is accompanied by an evolution or" oxygen:---

C9108!) 2=CaCla+02 In an acid solution, rapid decomposition occurs with the evolution of chlorine which I have found can result in chlorination oi the material being bleached and a consequent loss in strength.

When usual alkalies as caustic soda, soda ash, alkali phosphates, etc, are added to calcium bleach solutions, precipitation of the rather insoluble calcium hydroxide, carbonates or phosphate follows. The solution is clouded by the precipitate and, since a water clear solution is generally desirable, the use of these salts is limited to that amount corresponding to the saturation or" the solution with calcium hydroxide. This amount is equivalent to approximately one gram per liter of Cat). It has therefore been possible heretofore to add only a very small amount of alkali at any one time and the quantity added capable of remaining water clear ,and having a i high reserve alkalinity without danger oi forming precipitates of insoluble calcium salts.

in providing a calcium bleach solution capable of preserv ng its alkaline character even though contacted with a considerable volume of an acid producing material, i employ a borate; I have discovered that a borate buiiers the alkaline calcium bleach solutions satisfactorily. Thus the solutions maintain their alkalinity and concentrations of the borate can be employed which are far in excess of other salts utilized heretofore and without formation of a precipitate. As al- (Cls li -=23) kali borates both tetraborates and metaborates of the alkaline metals can be used as well as the more alkaline alkali metaborates. Boric acid can also be used, an alkali being added to neutralize the acid. The term borates" is used generically and is intended to comprise all the mentioned materials. The essential to the successful bufiering of the alkaline calcium salt solutions is the use of an alkaline salt soluble in the calcium bleach liquor to an appreciable extent and which does not form-a relatively insoluble calcium salt. ihe alkaline borates answer this test as do other alkali metal salts of weak acids which do not form insoluble calcium salts. Such other salts are alkali metal acetates and formates which are not expensive and can be usedsuccessfully. Other salts as the benzoates, butyrates, and salicylates can be used but are at this writing too expensive comparatively. As has been stated, the essential to the successful buffaring is the use of an alkaline bleach soluble in the calcium salt solution and not forming an insoluble calcium salt in the bleach solution. The particular use of the calcium bleach solution may add other necessary qualifications.

, Other objects and features of advantage thereof will appear in the following description of examples of processes and solutions embodying the invention.

A bleach liquor consisting of an aqueous solution of calcium hypochlorite and calcium chloride of a strength corresponding to 40 grams per liter available chloride, was treated by dissolving 10 pounds of bore in 100 gallons thereof, about 12 gms. per liter. This solution was used to bleach wood pulp, textiles and the like. The solution remained water clear during the bleaching process, retained'its alkalinity and the it is to be understood that the invention is not available chlorine and about 12 grams per liter of borax.

2. A water clear bleach liquorbuflered to retain its alkalinity and prevent free chlorine evolution comprising an aqueous calcium hypochlorite solution buffered with a borate.

3', The process of bleaching a material which comprises contacting said material with a solution of calcium hypochlorite buflered with a borate to maintain a. substantially constant alkalinity whereby said solution remains substantially water clear during bleaching of said material and evolution of free chlorine is substantially obviated.

4. Bleaching a material with an.- aqueous solution of a calcium hypochlorite buttered to neutralize all acid formed during said bleaching.

5. Bleaching a material with an aqueous caicium hypochlorite solution buiiered to maintain a constant pH during said bleaching and neutralize all acid formed during said bleaching.

6. Bleaching a wood pulp with an aqueous hypochlorite bleach while maintaining said bleach and pulp at a substantially constant pH on the alkaline side. f

7. Bleaching a wood pulp with an aqueous hypochlorite bleach, buttered to maintain said bleach and pulp at a substantially constant pH on the alkaline side.

8. Bleaching a material with an aqueous hypochlorite bleach buttered to maintain said bleach and said. material at a substantially con- 15 stant pH on the alkaline side. 

